Capacitive sensing array having electrical isolation

Abstract

A capacitive fingerprint sensor that may be formed of an array of sensing elements. Each capacitive sensing element of the array may register a voltage that varies with the capacitance of a capacitive coupling. A finger may capacitively couple to the individual capacitive sensing elements of the sensor, such that the sensor may sense a capacitance between each capacitive sensing element and the flesh of the fingerprint. The capacitance signal may be detected by sensing the change in voltage on the capacitive sensing element as the relative voltage between the finger and the sensing chip is changed. Alternately, the capacitance signal may be detected by sensing the change in charge received by the capacitive sensing elements as the relative voltage between the finger and the sensing chip is changed.

We claim: 
     
       1. An electronic device, comprising:
 a sensor chip comprising an array of individual capacitive sensing elements; 
 an antenna electronic component positioned within the electronic device; and 
 an electrical isolation wall electrically separating the sensor chip and the antenna, wherein: 
 the electrical isolation wall filters high frequency signals from traveling between the antenna and the sensor chip, and comprises a first inductor in series with a voltage supply of the sensor chip and a second inductor in series with a ground reference of the sensor chip. 
 
     
     
       2. The electronic device of  claim 1 , wherein the electrical isolation wall comprises at least one electrical component electrically connected to the sensor chip. 
     
     
       3. The electronic device of  claim 2 , wherein the electrical isolation wall is electrically connected to a controller chip, the controller chip operative to provide the voltage supply to the sensor chip. 
     
     
       4. The electronic device of  claim 3 , wherein:
 the voltage supply is a first voltage supply and 
 the controller chip is further operative to provide a second voltage supply to the sensor chip. 
 
     
     
       5. The electronic device of  claim 4 , wherein:
 the first inductor is connected in series between the controller chip and the first voltage supply of the sensor chip; and 
 a third inductor is connected in series between the controller chip and the second voltage supply of sensor chip. 
 
     
     
       6. The electronic device of  claim 5 , wherein:
 a clock of the controller chip is electrically coupled to a clock of the sensor chip. 
 
     
     
       7. The electronic device of  claim 6 , further comprising a resistor in series between the clock of the controller chip and the clock of the sensor chip. 
     
     
       8. The electronic device of  claim 7 , wherein the electrical isolation wall further comprises the third inductor and the resistor. 
     
     
       9. The electronic device of  claim 8 , wherein the antenna comprises a cellular antenna. 
     
     
       10. An electronic device, comprising:
 a housing; 
 an antenna at least partially within the housing; 
 an input element separate from the housing; 
 a sensor positioned beneath the input element; 
 a controller chip electrically connected to the sensor; and 
 an electrical isolation element electrically isolating the antenna from the sensor, the electrical isolation element comprising:
 a first inductor in series with a voltage supply of the sensor; and 
 a second inductor in series with a ground reference of the sensor. 
 
 
     
     
       11. The electronic device of  claim 10 , wherein the sensor is a biometric sensor. 
     
     
       12. The electronic device of  claim 10 , wherein the antenna comprises a cellular antenna. 
     
     
       13. The electronic device of  claim 12 , wherein the electrical isolation element filters high-frequency signals from traveling between the sensor and the antenna. 
     
     
       14. The electronic device of  claim 13 , wherein a cutoff frequency of the electrical isolation element is approximately 100 MHz. 
     
     
       15. The electronic device of  claim 10 , wherein the electrical isolation element comprises a plurality of electronic components, at least one electronic component in series with each of a plurality of electrical connections between the controller chip and the sensor. 
     
     
       16. The electronic device of  claim 10 , further comprising a diode in series with the first inductor. 
     
     
       17. The electronic device of  claim 16 , further comprising a capacitor operative to supply voltage through the diode to the sensor at least momentarily during operation of the sensor. 
     
     
       18. The electronic device of  claim 17 , wherein the capacitor and diode are electrically coupled at a common node. 
     
     
       19. The electronic device of  claim 18 , wherein:
 capacitor is a first capacitor; and 
 the electronic device further comprises a second capacitor positioned between the diode and the ground reference of the controller chip. 
 
     
     
       20. The electronic device of  claim 19 , wherein the first capacitor, diode, and second capacitor are physically positioned to minimize an inductance of a current loop through the diode. 
     
     
       21. The electronic device of  claim 19 , wherein the second capacitor is positioned adjacent the diode in a silicon layout.